Control system and method with constant maximum current for power converter protection

ABSTRACT

System and method for protecting a power converter. The system includes a first comparator configured to receive a threshold signal and a first signal and to generate a comparison signal. The first signal is a sum of a second signal and a third signal, and the third signal is associated with an input current for a power converter. Additionally, the system includes a pulse-width-modulation generator configured to receive the comparison signal and generate a modulation signal in response to the comparison signal, and a switch configured to receive the modulation signal and control the input current for the power converter. An amplitude for the first signal becomes larger if an amplitude for the input voltage becomes larger. The second signal is generated by receiving an input voltage for the power converter, converting the received input voltage to a fourth signal, and converting the fourth signal to the second signal.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.______ (EastIP Ref. No. 05NI3133-1365-SMY), filed Aug. 18, 2005,entitled “Control System and Method with Constant Maximum Current forPower Converter Protection,” by inventors Lieyi Fang, Shifeng Zhao, BoLi, and Zhiliang Chen, commonly assigned, incorporated by referenceherein for all purposes.

Additionally, this application is related to U.S. patent applicationSer. No. 11/051,242 (Attorney Docket Number 025748-0000100US), commonlyassigned, incorporated by reference herein for all purposes.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

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REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

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BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a control system and method forover-current protection with constant maximum current. Merely by way ofexample, the invention has been applied to a power converter. But itwould be recognized that the invention has a much broader range ofapplicability.

Power converters are widely used for consumer electronics such asportable devices. The power converters can convert electric power fromone form to another form. As an example, the electric power istransformed from alternate current (AC) to direct current (DC), from DCto AC, from AC to AC, or from DC to DC. Additionally, the powerconverters can convert the electric power from one voltage level toanother voltage level.

The power converters include linear converters and switch-modeconverters. The switch-mode converters often use pulse-width-modulated(PWM) or pulse-frequency-modulated mechanisms. These mechanisms areusually implemented with a switch-mode controller including variousprotection components. These components can provide over-voltageprotection, over-temperature protection, and over-current protection(OCP). These protections can often prevent the power converters andconnected circuitries from suffering permanent damage.

For example, a power converter includes a power switch and transformerwinding that is in series with the power switch. The current flowingthrough the power switch and transformer winding may be limited by anOCP system. If the OCP system is not effective, the current can reach alevel at which damage to the power switch is imminent due to excessivecurrent and voltage stress at switching or thermal run-away duringoperation. For example, this current level can be reached when theoutput short circuit or over loading occurs. Consequently, the rectifiercomponents on the transformer secondary side are subject to permanentdamage due to excessive voltage and current stress in many offlineflyback converters. Hence an effective OCP system is important for areliable switch mode converter.

FIG. 1 is a simplified conventional switch mode converter withover-current protection. A switch mode converter 100 includes an OCPcomparator 110, a PWM controller component 120, a gate driver 130, apower switch 140, resistors 150, 152, 154, and 156, and a primarywinding 160. For example, the OCP comparator 110, the PWM controllercomponent 120, and the gate driver 130 are parts of a chip 180 for PWMcontrol. When the current of the primary winding is greater than alimiting level, the PWM controller component 120 turns off the powerswitch 140 and shuts down the switch mode power converter 100.

For switch mode converter, a cycle-by-cycle or pulse-by-pulse controlmechanism is often used for OCP. For example, the cycle-by-cycle controlscheme limits the maximum current and thus the maximum power deliveredby the switch mode converter. This limitation on maximum power canprotect the power converter from thermal run-away. Some conventional OCPsystems use an adjustable OCP threshold value based on line inputvoltage, but the actual limitation on maximum current and thus maximumpower is not always constant over a wide range of line input voltage.Other conventional OCP systems use additional resistors 152 and 154 thatare external to the chip 180 and inserted between V_(in) and theresistor 150 as shown in FIG. 1. But the resistor 152 consumessignificant power, which often is undesirable for meeting stringentrequirements on low standby power. For example, the resistor 152 of 2 MΩcan dissipate about 70 mW with input AC voltage of 264 volts.

Hence it is highly desirable to improve techniques for over-currentprotection.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a control system and method forover-current protection with constant maximum current. Merely by way ofexample, the invention has been applied to a power converter. But itwould be recognized that the invention has a much broader range ofapplicability.

According to one embodiment of the present invention, a system forprotecting a power converter is provided. The system includes a firstcomparator configured to receive a threshold signal and a first signaland to generate a comparison signal. The first signal is a sum of asecond signal and a third signal, and the third signal is associatedwith an input current for a power converter. Additionally, the systemincludes a pulse-width-modulation generator configured to receive thecomparison signal and generate a modulation signal in response to thecomparison signal, and a switch configured to receive the modulationsignal and control the input current for the power converter. Anamplitude for the first signal becomes larger if an amplitude for theinput voltage becomes larger. The second signal is generated byreceiving an input voltage for the power converter, converting thereceived input voltage to a fourth signal, and converting the fourthsignal to the second signal.

According to another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a firstsignal and a second signal and to generate a comparison signal. Thefirst signal is associated with an input current for a power converter.Additionally, the system includes a threshold generator configured toreceive at least a third signal and generate the second signal inresponse to at least the third signal. The third signal is associatedwith an input voltage for the power converter. Moreover, the systemincludes a pulse-width-modulation generator configured to receive thecomparison signal and generate a modulation signal in response to thecomparison signal, and a switch configured to receive the modulationsignal and control the input current for the power converter. Anamplitude for the second signal becomes smaller if an amplitude for theinput voltage becomes larger, and the third signal is generated byreceiving an input voltage for the power converter and converting thereceived input voltage to the third signal.

According to yet another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a thresholdsignal and a first signal and to generate a comparison signal. The firstsignal is equal to a second signal subtracted by a third signal, and thesecond signal is associated with an input current for a power converter.Additionally, the system includes a pulse-width-modulation generatorconfigured to receive the comparison signal and generate a modulationsignal in response to the comparison signal, and a switch configured toreceive the modulation signal and control the input current for thepower converter. Moreover, the system includes an oscillator coupled tothe pulse-width-modulation generator and configured to generate at leasta first control signal, a transconductor configured to receive the firstcontrol signal and generate a second control signal, and a currentsupplier configured to receive the second control signal and generate afirst current in response to the second control signal, the firstcurrent being associated with the third signal. An amplitude for thefirst current becomes smaller if an amplitude for the input voltagebecomes larger.

According to yet another embodiment, a method for protecting a powerconverter includes receiving an input voltage for a power converter,converting the received input voltage to a first signal, converting thefirst signal to a second signal, and generating a third signal based onat least information associated with the second signal. Additionally,the method includes receiving the third signal and a threshold signal.The third signal is a sum of the second signal and a fourth signal, andthe fourth signal is associated with an input current for the powerconverter. Moreover, the method includes generating a comparison signalbased on at least information associated with the third signal and thethreshold signal, and processing information associated with thecomparison signal. Also, the method includes generating a modulationsignal based on at least information associated with the comparisonsignal, and controlling the input current for the power converter inresponse to the modulation signal. An amplitude for the third signalbecomes larger if an amplitude for the input voltage becomes larger.

According to yet another embodiment, a method for protecting a powerconverter includes receiving an input voltage for a power converter,converting the received input voltage to a first signal, processinginformation associated with the first signal, generating a second signalbased on at least information associated with the first signal, andreceiving the second signal and a third signal. The third signal isassociated with an input current for a power converter. Additionally,the method includes generating a comparison signal based on at leastinformation associated with the second signal and the third signal,processing information associated with the comparison signal, generatinga modulation signal based on at least information associated with thecomparison signal, and controlling the input current for the powerconverter in response to the modulation signal. An amplitude for thesecond signal becomes smaller if an amplitude for the input voltagebecomes larger.

According to yet another embodiment, a method for protecting a powerconverter includes generating a first signal based on at leastinformation associated with an input current for a power converter,generating a second signal, the second signal being proportional to aramping current, and processing information associated with the firstsignal and the second signal. Additionally, the method includesgenerating a third signal equal to the first signal subtracted by thesecond signal, receiving the third signal and a threshold signal,generating a comparison signal based on at least information associatedwith the third signal and the threshold signal, processing informationassociated with the comparison signal, generating a modulation signalbased on at least information associated with the comparison signal, andcontrolling the input current for the power converter in response to themodulation signal. An amplitude for the ramping current corresponding toa predetermined value for the input current becomes smaller if anamplitude for the input voltage becomes larger.

Many benefits are achieved by way of the present invention overconventional techniques. For example, some embodiments can provide anexcellent compensation for the “delay to output” by easily adjusting anexternal resistor. For example, the adjustment of the external resistortakes into account converter components external to a chip for PWMcontrol. Certain embodiments allow a maximum current and a maximum powerthat are constant over a wide range of input voltage. Some embodimentsconsume a low standby power by sharing a resistor for a sensing systemwith a startup system and/or a brownout protection system. For example,the resistor is shared by a sensing system and a startup system. Certainembodiments provide an excellent compensation for the “delay to output”without sensing an input voltage. For example, the pin counts for a chipfor PWM control is limited. In another example, the maximum width of aPWM signal is used to represent the input voltage. Different inputvoltages result in different maximum widths for the PWM signal, and thedifferent maximum widths result in different effective thresholdsignals. Some embodiments provide an over-current protection that caneffectively protect a power converter from excessive power, thermal runaway, excessive current and/or voltage stress.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and the accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified conventional switch mode converter withover-current protection;

FIG. 2 is a simplified diagram showing relationship between extracurrent ramping amplitude and line input voltage;

FIG. 3 is a simplified diagram showing relationship between currentthreshold and line input voltage;

FIG. 4 is a simplified diagram showing relationship between thresholdoffset and line input voltage;

FIG. 5 is a simplified control system with constant maximum currentaccording to an embodiment of the present invention;

FIG. 6 is a simplified control system with constant maximum currentaccording to an embodiment of the present invention;

FIG. 7 is a simplified control system with constant maximum currentaccording to another embodiment of the present invention;

FIG. 8 is a simplified control system with constant maximum currentaccording to yet another embodiment of the present invention;

FIG. 9 is a simplified control system with constant maximum currentaccording to yet another embodiment of the present invention;

FIG. 10 is a simplified diagram showing relationship between PWM signalmaximum width and input voltage according to an embodiment of thepresent invention;

FIG. 11 is a simplified control system with constant maximum currentaccording to yet another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to integrated circuits. Moreparticularly, the invention provides a control system and method forover-current protection with constant maximum current. Merely by way ofexample, the invention has been applied to a power converter. But itwould be recognized that the invention has a much broader range ofapplicability.

As shown in FIG. 1, the current limit is expressed as follows:$\begin{matrix}{I_{Limit} = {{\frac{V_{i\quad n}}{L_{p}} \times t_{on}} = \frac{V_{th\_ oc}}{R_{s}}}} & \left( {{Equation}\quad 1} \right)\end{matrix}$

where I_(Limit) represents the current limit. For example, the currentlimit is the current threshold for triggering over-current protection.Additionally, V_(in) is the input line voltage at node 190, and V_(th)_(—) _(oc) is the voltage level at an input terminal 112 of the OCPcomparator 110. R_(s) is the resistance of the resistor 150, and L_(p)is the inductance of the primary winding 160. Moreover, t_(on)represents on time of the power switch 140 for each cycle. Accordingly,the maximum energy ε stored in the primary winding 160 is$\begin{matrix}{ɛ = {{\frac{1}{2} \times L_{p} \times I_{Limit}^{2}} = {PT}}} & \left( {{Equation}\quad 2} \right)\end{matrix}$

where T represents the clock period, and P represents the maximum power.So the maximum power P can be expressed as follows: $\begin{matrix}{P = {\frac{L_{p} \times I_{Limit}^{2}}{2T} = \frac{V_{i\quad n} \times t_{on}^{2}}{2 \times L_{p} \times T}}} & \left( {{Equation}\quad 3} \right)\end{matrix}$

Therefore the power can be limited by controlling the current limitI_(Limit). But Equation 3 does not take into account the “delay tooutput” that includes the propagation delay through a current sense pathto the power switch 140. For example, the propagation delay includespropagation delays through the OCP comparator 110, the PWM controllercomponent 120, the gate driver 130, and the response delay of turningoff of the power switch 140. During the “delay to output,” the powerswitch 140 remains on, and the input current through the switch 140keeps ramping up despite the current has already reached the thresholdlevel of the OCP comparator 110. The extra current ramping amplitude,ΔI, due the “delay to output” is proportional to the line input voltageV_(in) as follows: $\begin{matrix}{{\Delta\quad I} = {\frac{V_{i\quad n}}{L_{p}} \times T_{delay}}} & \left( {{Equation}\quad 4} \right)\end{matrix}$

where T_(delay) represents the “delay to output.” FIG. 2 is a simplifieddiagram showing relationship between extra current ramping amplitude andline input voltage. As shown in FIG. 2, the actual maximum currentI_(PEAK1) that corresponds to higher V_(in) is larger than the actualmaximum current I_(PEAK2) that corresponds to lower V_(in). Accordingly,the actual maximum power is not constant over a wide range of line inputvoltage. Hence the actual maximum power is expressed as follows:$\begin{matrix}{P = {\frac{L_{p} \times \left( {I_{Limit} + {\Delta\quad I}} \right)^{2}}{2T} = \frac{V_{i\quad n} \times \left( {t_{on} + T_{delay}} \right)^{2}}{2 \times L_{p} \times T}}} & \left( {{Equation}\quad 5} \right)\end{matrix}$

For example, T_(delay) depends on internal delays, gate charges, andcircuitry related to the gate driver 130. In another example, for thepredetermined switch mode converter 100, T_(delay) is constant, andhence the actual maximum power depends on the line input voltage. Tocompensate for variations of the actual maximum power, the threshold forover-current protection should be adjusted based on the input linevoltage.

FIG. 3 is a simplified diagram showing relationship between currentthreshold and line input voltage. The line input voltage V_(in2) islower than the line input voltage V_(in1), and the current thresholdI_(th) _(—) _(oc) _(—) _(vin2) for V_(in2) is larger than I_(th) _(—)_(oc) _(—) _(vin1) for V_(in1) as shown in FIG. 3. The current thresholddecreases with increasing line input voltage V_(in). At the currentthreshold, the over-current protection is triggered. The resultingmaximum current I_(PEAK1) for higher V_(in) is the same as the resultingmaximum current I_(PEAK2) for lower V_(in).

For example, the current threshold has the following relationship withthe line input voltage: $\begin{matrix}{I_{th\_ oc} \approx {{I_{th\_ oc}\left( V_{i\quad n\quad 1} \right)} - {\frac{V_{i\quad n} - V_{i\quad n\quad 1}}{L_{p}}T_{delay}}}} & \left( {{Equation}\quad 6} \right)\end{matrix}$

where I_(th) _(—) _(oc) is the current threshold, V_(in) is the lineinput voltage, L_(p) is the inductance of the primary winding, andT_(delay) is the “delay to output. Additionally, I_(th) _(—)_(oc)(V_(in1)) is the current threshold that is predetermined for theinput line voltage V_(in1). For example, V_(in1) is the minimum lineinput voltage. In another example, the current is sensed that flowsthrough the power switch and the primary winding. If the sensed currentreaches I_(th) _(—) _(oc), the PWM controller component sends a signalto turn off the power switch. After “delay to output,” the power switchis turned off.

In Equation 6, the second term$\frac{V_{i\quad n} - V_{i\quad n\quad 1}}{L_{p}}T_{delay}$represents a threshold offset to compensate for the effects of “delay tooutput.” FIG. 4 is a simplified diagram showing relationship betweenthreshold offset and line input voltage. As shown in FIG. 4, the term$\frac{T_{delay}}{L_{p}}$is the slop that depends on the “delay to output” and the inductance ofprimary winding. As shown in FIG. 4, the current threshold decreaseswith increasing line input voltage.

For certain applications, it is difficult to estimate the thresholdoffset on chip for PWM control in order to compensate for the “delay tooutput.” For example, T_(delay) depends on converter components that areinternal and as well as external to the chip. The external componentsmay include a power MOSFET. Different types of power MOSFETs can havedifferent gate charges, which in turn result in different “delays tooutput.” Also, the external components may include the primary winding.Different types of primary windings can have different inductancevalues. In another example, the gate driver on the chip is intentionallymade slow for longer T_(delay).

Certain embodiments of the present invention provide systems and methodsthat allow maximum currents that are constant over wide range of inputvoltage. For example, these systems and methods are implemented inswitch mode converters. In another example, the input voltage is theinput line voltage for power converters.

In some embodiments, the input voltage is sensed and used to control acurrent source. The current source outputs a current that is used togenerate an offset signal through an adjustable resistor. For example,the adjustable resistor is external to a chip for PWM control. Theoffset signal is superimposed on a current sensing signal, and thissuperimposition provides a threshold offset to a predetermined currentthreshold as shown in Equation 6.

These embodiments of the present invention include examples of FIGS. 5through 9. FIGS. 5-9 are simplified control systems with constantmaximum current according to certain embodiments of the presentinvention. These diagrams are merely examples, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications.

As shown in FIGS. 5-7, an input voltage V_(in) is sensed and used tocontrol a current source. The current source generates a currentI_(—vin) as follows: $\begin{matrix}{I_{\_ vin} = {\alpha\frac{V_{i\quad n}}{R_{sv}}}} & \left( {{Equation}\quad 7} \right)\end{matrix}$

where α is a constant. The current I_(—vin) is used to generate anoffset signal through an adjustable resistor R. For FIGS. 5 and 6, theoffset signal is superimposed to a current sensing signal. Accordingly,an input signal to a comparator is the summation of sensed signalI_(sense)×R_(s) and the offset signal I_(—vin)×R. If the input signalreaches the threshold signal V_(th) _(—) _(oc), a gate driver iscommanded to turn off a power switch. Accordingly, when the over-currentprotection is triggered,I _(sense) ×R _(s) +I _(—vin) ×R=V _(th) _(—) _(oc)  (Equation 8A)

The effective threshold signal I_(th) _(—) _(oc) is $\begin{matrix}{I_{th\_ oc} = \frac{I_{sense}}{R_{s}}} & \left( {{Equation}\quad 9} \right) \\{{Therefore},\begin{matrix}{I_{th\_ oc} = {\frac{V_{th\_ oc}}{R_{s}} - \frac{I_{\_ vin} \times R}{R_{s}}}} \\{= {\frac{V_{th\_ oc}}{R_{s}} - \frac{\alpha \times {Vin} \times R}{R_{s} \times R_{sv}}}}\end{matrix}} & \left( {{Equation}\quad 10} \right)\end{matrix}$

From Equations 6 and 10, the following relationship can be derived:$\begin{matrix}{{{I_{th\_ oc}\left( V_{{in}\quad 1} \right)} = {\frac{V_{th\_ oc}}{R_{s}} - {\frac{V_{{in}\quad 1}}{L_{p}}T_{delay}}}}{and}} & \left( {{Equation}\quad 11} \right) \\{{{\frac{V_{in}}{L_{p}}T_{delay}} = \frac{\alpha \times V_{in} \times R}{R_{s} \times R_{sv}}}{According}} & \left( {{Equation}\quad 12} \right) \\{R = {\frac{R_{s} \times R_{sv}}{\alpha\quad L_{p}}T_{delay}}} & \left( {{Equation}\quad 13} \right)\end{matrix}$

Hence the effects of “delay to output” can be compensated by adjustingthe resistor R for given L_(p), R_(sv), and R_(s) in a switching modeconverter.

For FIG. 7, the offset signal is subtracted from the threshold signal togenerate an effective threshold signal V_(th) _(—) _(oc) _(—) _(eff).The effective threshold signal is provided to a comparator. Anotherinput of the comparator receives the sensed signal I_(sense)×R_(s). Ifthe sensed signal reaches the effective threshold signal V_(th) _(—)_(oc) _(—) _(eff), a gate driver is commanded to turn off a powerswitch. Accordingly, when the over-current protection is triggered,I _(sense) ×R _(s) =V _(th) _(—) _(oc) _(—) _(eff) =V _(th) _(—) _(oc)−I _(—vin) ×R  (Equation 8B)

Therefore, Equations 9-13 are still valid. The effects of “delay tooutput” can be compensated by adjusting the resistor R for given L_(p),R_(sv), and R_(s) in a switching mode converter.

FIG. 5 is a simplified control system with constant maximum currentaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. A system 500 includesresistors 510, 512, and 514, current suppliers 520 and 522, a startupsystem 552, a comparator 530, a pulse-width-modulation (PWM) generator540, a sensing system 550, a threshold generator 560, and a switch 570.Although the above has been shown using a selected group of componentsfor the system 500, there can be many alternatives, modifications, andvariations. For example, some of the components may be expanded and/orcombined. Other components may be inserted to those noted above. Forexample, the system 500 includes an oscillator 580, which sends a clocksignal and a ramping signal to the PWM generator 540. In anotherexample, the system 500 includes a primary winding 582 with aninductance value of L_(p). Depending upon the embodiment, thearrangement of components may be interchanged with others replaced. Forexample, the system 500 is used to regulate a power converter. Furtherdetails of these components are found throughout the presentspecification and more particularly below.

For example, an input voltage V_(in) at node 590 is sensed by thesensing system 550 through the resistor 512 of R_(sv). In oneembodiment, the resistor 512 has a resistance value ranging from severalhundred kilo-ohms to several mega-ohms. In another embodiment, thesensing system 550 sends a signal to the current supplier 520. Forexample, the current supplier 520 is a current source. The currentsupplier 520 generates a current I_(—vin) flowing through the resistor510 of R and generating an offset signal. The offset signal issuperimposed to a current sensing signal. For example, the currentsensing signal is generated by the resistor 514 of R_(s). The summationof the offset signal and the current sensing signal is provided to aninput 532 of the comparator 530. For example, the summation is in thevoltage domain. At the comparator 530, the summation is compared with apredetermined threshold signal generated by the threshold generator 560.For example, the threshold generator 560 receives a current I_(—vin1)and a reference voltage V_(ref). Based on the comparison, the comparator530 sends a signal to the PWM generator 540. For example, the PWMgenerator 540 includes a PWM comparator 542, a logic controller 544, anda gate driver 546. The logic controller receives the signal sent fromthe comparator 530. In another example, the PWM comparator 542 receivesthe clock signal and the ramping signal generated by the oscillator 580.The PWM generator 540 receives the signal from the comparator 530 andcontrols the switch 570 through the gate driver 546. Additionally, thesensing system 550 sends a signal to the current supplier 522 accordingto an embodiment of the present invention. For example, the currentsupplier 522 is a current source. The current supplier 522 generates thecurrent I_(—vin1) received by the threshold generator 560. The effectsof “delay to output” can be compensated by adjusting the resistor R. Forexample, the system 500 allows a maximum current that is constant over awide range of the input voltage V_(in). In another example, the resistor510 is adjusted for given L_(p), R_(sv), and R_(s) in a switching modeconverter according to Equation 13. In yet another example, the startupsystem 552 is connected to the sensing system 550, and is used tocontrol powering up of a chip for PWM control.

FIG. 6 is a simplified control system with constant maximum currentaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. A system 600 is an exampleof the system 500. As shown in FIG. 6, the input voltage V_(in) at thenode 590 is converted by the resistor 512 of R_(sv) into a current. Thecurrent is sensed by a transistor 610 of MP1 through a voltage VDD atnode 620. For example, the node 620 is connected to a capacitor 630 ofC1, which is charged by the input voltage V_(in) and used to start upthe chip for PWM control. In another example, the current I sensed bythe transistor 620 is $\begin{matrix}{I = {\frac{V_{in} - {VDD}}{R_{sv}} \approx \frac{V_{in}}{R_{sv}}}} & \left( {{Equation}\quad 14} \right)\end{matrix}$

where VDD is negligible in comparison with V_(in). Therefore the sensedcurrent I is a function of the input voltage V_(in). As shown in FIG. 6,the sensed current is mirrored by another transistor 612 of MP2 togenerate another current I1. For example, the current mirror includesboth the transistors 610 and 612. The current I1 is further mirrored bya transistor 614 of MN1 and a transistor 616 of MN2 to generate acurrent I2. The current I2 is mirrored by a transistor 618 of MP3 and atransistor 619 of MP4 to generate a current I_(—vin). For example, thecascade transistors are used to boost the output impedance of thecurrent mirrors. In another example, the current I_(—vin) isproportional to the current I sensed by the transistor 620. The currentI_(—vin) is used to generate the offset signal through the resistor 510of R. The offset signal is superimposed to the current sensing signal.The generated signal V_(cs) at node 622 isV _(cs) =I _(sense) ×R _(s) +I _(—vin) ×R  (Equation 15)

As shown in FIG. 6, the signal V_(cs) is provided to an input 532 of thecomparator 530. At the comparator 530, the signal V_(cs) is comparedwith a predetermined threshold signal generated by the thresholdgenerator 560. In response, the comparator 530 sends a signal to the PWMgenerator 540, which controls the switch 570. Additionally, transistors640 and 642 generate the current I_(—vin1), which is received by thethreshold generator 560.

FIG. 7 is a simplified control system with constant maximum currentaccording to another embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. A system 700 includesresistors 710, 712, and 714, a current supplier 720, a startup system752, a comparator 730, a pulse-width-modulation (PWM) generator 740, asensing system 750, a threshold generator 760, and a switch 770.Although the above has been shown using a selected group of componentsfor the system 700, there can be many alternatives, modifications, andvariations. For example, some of the components may be expanded and/orcombined. Other components may be inserted to those noted above. Forexample, the system 700 includes an oscillator 780, which sends a clocksignal and a ramping signal to the PWM generator 740. In anotherexample, the system 700 includes a primary winding 782 with aninductance value of L_(p). In yet another embodiment, the system 700includes a signal generator 762 for providing a voltage referencesignal. Depending upon the embodiment, the arrangement of components maybe interchanged with others replaced. For example, the system 700 isused to regulate a power converter. Further details of these componentsare found throughout the present specification and more particularlybelow.

For example, an input voltage V_(in) at node 790 is sensed by thesensing system 750 through the resistor 712 of R_(sv). In oneembodiment, the resistor 712 has a resistance value ranging from severalhundred kilo-ohms to several mega-ohms. In another embodiment, thesensing system 750 receives a signal from the startup system 752, andsends a signal to the current supplier 720. For example, the startupsystem 752 is connected to the input voltage V_(in) through the resistor712, and is used to control powering up of a chip for PWM control. Inanother example, the current supplier is a current source. The currentsupplier generates a current I_(—vin) flowing through the resistor 710of R and generating an offset signal. For example, the offset signal isan offset voltage. The offset signal is provided to the thresholdgenerator 760, which also receives a voltage reference signal from thesignal generator 762. The threshold generator 760 provides an effectivethreshold signal v_(th) _(—) _(oc) _(—) _(eff) to an input 734 of thecomparator 730. Additionally, a current sensing signal is received by aninput 732 of the comparator 730. For example, the current sensing signalis generated by the resistor 714 of R_(s). In another example, thecurrent sensing signal is in the voltage domain.

At the comparator 730, the current sensing signal is compared with theeffective threshold signal V_(th) _(—) _(oc) _(—) _(eff). Based on thecomparison, the comparator 730 sends a signal to the PWM generator 740.For example, the PWM generator 740 includes a PWM comparator 742, alogic controller 744, and a gate driver 746. The logic controllerreceives the signal sent from the comparator 730. In another example,the PWM comparator 742 receives the clock signal and the ramping signalgenerated by the oscillator 780. The PWM generator 740 receives thesignal from the comparator 730 and controls the switch 770 through thegate driver 746. The effects of “delay to output” can be compensated byadjusting the resistor R. For example, the system 700 allows a maximumcurrent that is constant over a wide range of the input voltage V_(in).In another example, the resistor R is adjusted for given L_(p), R_(sv)and R_(s) in a switching mode converter according to Equation 13.

According to other embodiments of the present invention, an inputvoltage V_(in) is sensed and used to control a current source as shownin FIGS. 8 and 9. The current source generates a current I_(—vin) asfollows:or I _(—vin) =βV _(in)  (Equation 14)

where β is a constant. The current I_(—vin) is used to generate anoffset signal through an adjustable resistor R. For FIG. 8, the offsetsignal is superimposed to a current sensing signal. Accordingly, aninput signal to a comparator is the summation of sensed signalI_(sense)×R_(s) and the offset signal I_(—vin)×R. If the input signalreaches the threshold signal V_(th) _(—) _(oc), a gate driver iscommanded to turn off a power switch. Accordingly, when the over-currentprotection is triggered,I _(sense) ×R _(s) +I _(—vin) ×R=V _(th) _(—) _(oc)  (Equation 15A)

The effective threshold signal I_(th) _(—) _(oc) is $\begin{matrix}{{I_{th\_ oc} = \frac{I_{sense}}{R_{s}}}{{Therefore},}} & \left( {{Equation}\quad 16} \right) \\{I_{th\_ oc} = {{\frac{V_{th\_ oc}}{R_{s}} - \frac{I_{\_ vin} \times R}{R_{s}}} = {\frac{V_{th\_ oc}}{R_{s}} - \frac{\beta \times V_{in} \times R}{R_{s}}}}} & \left( {{Equation}\quad 17} \right)\end{matrix}$

From Equations 6 and 17, the following relationship can be derived:$\begin{matrix}{{{I_{th\_ oc}\left( V_{{in}\quad 1} \right)} = {\frac{V_{th\_ oc}}{R_{s}} - {\frac{V_{{in}\quad 1}}{L_{p}}T_{delay}}}}{and}} & \left( {{Equation}\quad 18} \right) \\{{{\frac{V_{in}}{L_{p}}T_{delay}} = \frac{\beta \times V_{in} \times R}{R_{s}}}{According}} & \left( {{Equation}\quad 19} \right) \\{R = {\frac{R_{s}}{\beta\quad L_{p}}T_{delay}}} & \left( {{Equation}\quad 20} \right)\end{matrix}$

Hence the effects of “delay to output” can be compensated by adjustingthe resistor R for given L_(p) and R_(s) in a switching mode converter.

For FIG. 9, the offset signal is subtracted from the threshold signal togenerate an effective threshold signal V_(th) _(—) _(oc) _(—) _(eff).The effective threshold signal is provided to a comparator. Anotherinput of the comparator receives the sensed signal I_(sense)×R_(s). Ifthe sensed signal reaches the effective threshold signal V_(th) _(—)_(oc) _(—) _(eff), a gate driver is commanded to turn off a powerswitch. Accordingly, when the over-current protection is triggered,I _(sense) ×R _(s) =V _(th) _(—) _(oc) _(—) _(eff) =V _(th) _(—) _(oc)−I _(—vin) ×R  (Equation 15B)

Therefore, Equations 16-20 are still valid. The effects of “delay tooutput” can be compensated by adjusting the resistor R for given L_(p)and R_(s) in a switching mode converter.

FIG. 8 is a simplified control system with constant maximum currentaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. A system 800 includesresistors 810, 811, 812, and 814, a comparator 830, apulse-width-modulation (PWM) generator 840, a sensing system 850, atransconductor 852, a threshold generator 860, and a switch 870.Although the above has been shown using a selected group of componentsfor the system 800, there can be many alternatives, modifications, andvariations. For example, some of the components may be expanded and/orcombined. Other components may be inserted to those noted above. Forexample, the system 800 includes an oscillator, which sends a clocksignal and a ramping signal to the PWM generator 840. In anotherexample, the system 800 includes a primary winding 882 with aninductance value of L_(p). In yet another example, the system 800includes a brownout protection system 854. Depending upon theembodiment, the arrangement of components may be interchanged withothers replaced. For example, the system 800 is used to regulate a powerconverter. Further details of these components are found throughout thepresent specification and more particularly below.

For example, an input voltage V_(in) at node 890 is received by avoltage divider to generate a voltage βV_(in). For example, the voltagedivider includes the resistors 811 and 812, which are external to thechip for PWM control. The voltage βV_(in) is received by the sensingsystem 850 to generate a voltage signal. The voltage signal is sent tothe transconductor 852, which generates a current I_(—vin) flowingthrough the resistor 810 of R and generating an offset signal. Forexample, the transconductor 852 is a voltage-controlled current source.The offset signal is superimposed to a current sensing signal. Forexample, the current sensing signal is generated by the resistor 814 ofR_(s). The summation of the offset signal and the current sensing signalis provided to an input 832 of the comparator 830. For example, thesummation is in the voltage domain. At the comparator 830, the summationis compared with a predetermined threshold signal generated by thethreshold generator 860. Based on the comparison, the comparator 830sends a signal to the PWM generator 840. For example, the PWM generator840 includes a PWM comparator 842, a logic controller 844, and a gatedriver 846. The logic controller receives the signal sent from thecomparator 830. In another example, the PWM comparator 842 receives theclock signal and the ramping signal generated by the oscillator. The PWMgenerator 840 receives the signal from the comparator 830 and controlsthe switch 870 through the gate driver 846. The effects of “delay tooutput” can be compensated by adjusting the resistor R. For example, thesystem 800 allows a maximum current that is constant over a wide rangeof the input voltage V_(in). In another example, the resistor 810 isadjusted for given L_(p) and R_(s) in a switching mode converteraccording to Equation 20. In yet another example, the brownoutprotection system 854 receives the voltage βV_(in), and is used toprotect a switch-mode converter if an input voltage falls below apredetermined value.

FIG. 9 is a simplified control system with constant maximum currentaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. A system 900 includesresistors 910, 911, 912, and 914, a comparator 930, apulse-width-modulation (PWM) generator 940, a sensing system 950, atransconductor 952, a threshold generator 960, and a switch 970.Although the above has been shown using a selected group of componentsfor the system 900, there can be many alternatives, modifications, andvariations. For example, some of the components may be expanded and/orcombined. Other components may be inserted to those noted above. Forexample, the system 900 includes an oscillator, which sends a clocksignal and a ramping signal to the PWM generator 940. In anotherexample, the system 900 includes a primary winding 982 with aninductance value of L_(p). In yet another example, the system 900includes a brownout protection system 954. In yet another embodiment,the system 900 includes a signal generator 962 for providing a voltagereference signal. Depending upon the embodiment, the arrangement ofcomponents may be interchanged with others replaced. For example, thesystem 900 is used to regulate a power converter. Further details ofthese components are found throughout the present specification and moreparticularly below.

For example, an input voltage V_(in) at node 990 is received by avoltage divider to generate a voltage βV_(in). For example, the voltagedivider includes the resistors 911 and 912, which are external to thechip for PWM control. The voltage βV_(in) is received by the sensingsystem 950 to generate a voltage signal. The voltage signal is sent tothe transconductor 952, which generates a current I_(—vin) flowingthrough the resistor 910 of R and generating an offset signal. Forexample, the transconductor 852 is a voltage-controlled current source.In another example, the offset signal is an offset voltage. The offsetsignal is provided to the threshold generator 960, which also receives avoltage reference signal from the signal generator 962. The thresholdgenerator 960 provides an effective threshold signal V_(th) _(—) _(oc)_(—) _(eff) to an input 934 of the comparator 930. Additionally, acurrent sensing signal is received by an input 932 of the comparator930. For example, the current sensing signal is generated by theresistor 914 of R_(s). In another example, the current sensing signal isin the voltage domain.

At the comparator 930, the current sensing signal is compared with theeffective threshold signal V_(th) _(—) _(oc) _(—) _(eff). Based on thecomparison, the comparator 930 sends a signal to the PWM generator 940.For example, the PWM generator 940 includes a PWM comparator 942, alogic controller 944, and a gate driver 946. The logic controllerreceives the signal sent from the comparator 930. In another example,the PWM comparator 942 receives the clock signal and the ramping signalgenerated by the oscillator. The PWM generator 940 receives the signalfrom the comparator 930 and controls the switch 970 through the gatedriver 946. The effects of “delay to output” can be compensated byadjusting the resistor R. For example, the system 900 allows a maximumcurrent that is constant over a wide range of the input voltage V_(in).In another example, the resistor R is adjusted for given L_(p) and R_(s)in a switching mode converter according to Equation 20. In yet anotherexample, the brownout protection system 954 receives the voltageβV_(in), and is used to protect a switch-mode converter if an inputvoltage falls below a predetermined value.

According to other embodiments of the present invention, an inputvoltage is sensed based on the maximum width of PWM signal. For example,the PWM signal is applied to the gate of a power switch in series to theprimary winding of a power converter. FIG. 10 is a simplified diagramshowing relationship between PWM signal maximum width and input voltageaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. As shown in FIG. 5, themaximum current is constant with respect to input voltage, and themaximum width of PWM signal varies with the input voltage. For example,the input voltage is the input line voltage for power converter. Inanother example, the maximum current I_(PEAK1) equals the maximumcurrent I_(PEAK2). The maximum current I_(PEAK1) corresponds to a higherinput voltage and a PWM signal 510, and the maximum current I_(PEAK2)corresponds to a lower input voltage and a PWM signal 520. As shown inFIG. 5, the maximum width for the PWM signal 510 is narrower for higherinput voltage, and the maximum width for PWM signal 520 is wider forlower input voltage. The input voltage is represented by the maximumwidth of PWM signal if the maximum current is constant with respect toinput voltage. Accordingly, the maximum width of PWM signal can be usedto determine the threshold offset to compensate for the effects of“delay to output” as shown in Equation 6.

In one embodiment, the compensation can be realized by generating acurrent threshold, I_(th) _(—) _(oc), which is a function of the maximumwidth of PWM signal as shown in FIG. 10. For example, the currentthreshold is equal to I_(th) _(—) _(oc) _(—) ₁ for the PWM signal 510and I_(th) _(—) _(oc) _(—) ₂ for the PWM signal 520. In another example,the slope of I_(th) _(—) _(oc) with respect to the maximum width isproperly chosen to compensate for the effects of “delay to output”according to Equation 6. The selected slope takes into accountinformation about power converter components that are external to thechip for PWM control. For example, the external components include theprimary winding, a current sensing resistor and a power MOSFET. Thisembodiment of the present invention includes certain examples of FIG.11.

FIG. 11 is a simplified control system with constant maximum currentaccording to yet another embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. A system 1100 includesresistors 1110, 1112, 1114, and 1116, a current supplier 1120, a startupsystem 1152, a comparator 1130, a pulse-width-modulation (PWM) generator1140, a threshold generator 1160, and a switch 1170. Although the abovehas been shown using a selected group of components for the system 1100,there can be many alternatives, modifications, and variations. Forexample, some of the components may be expanded and/or combined. Othercomponents may be inserted to those noted above. For example, the system1100 includes an oscillator 1180, which sends a clock signal and aramping signal to the PWM generator 1140. In another example, the system1100 includes a primary winding 1182 with an inductance value of L_(p).Depending upon the embodiment, the arrangement of components may beinterchanged with others replaced. For example, the system 1100 is usedto regulate a power converter. In another example, the resistor 1116 ofR_(comp) is removed. Further details of these components are foundthroughout the present specification and more particularly below.

The current supplier 1120 is connected to the resistor 1116 of R_(comp),and is used to generate a current I_(—comp). For example, the currentsupplier 1120 is a current sink. In another example, the currentsupplier 1120 includes a transconductor. In yet another example, thecurrent I_(—comp) is a ramping current that is synchronized with a PWMsignal. The current I_(—comp) flows through the resistor 1116 ofR_(comp) and the resistor 1110 of R and generates an offset signal. Forexample, the offset signal is in the voltage domain. The offset signalis subtracted from a current sensing signal to generate a compositesignal. For example, the current sensing signal is generated by theresistor 1114 of R_(s). The composite signal is provided to an input1132 of the comparator 1130. For example, the composite signal is in thevoltage domain and represented by V_(com). At the comparator 1130, thecomposite signal is compared with a predetermined threshold signalgenerated by the threshold generator 1160. For example, thepredetermined threshold signal is the threshold voltage V_(th) _(—)_(oc). Based on the comparison, the comparator 1130 sends a signal tothe PWM generator 1140. For example, the PWM generator 1140 includes aPWM comparator 1142, a logic controller 1144, and a gate driver 1146.The logic controller receives the signal sent from the comparator 1130.In another example, the PWM comparator 1142 receives the clock signaland the ramping signal generated by the oscillator 1180. The PWMgenerator 1140 receives the signal from the comparator 1130 and controlsthe switch 1170 through the gate driver 1146. For example, the gatedriver 1146 generates the PWM signal. The startup system 1152 isconnected to the input voltage V_(in) through the resistor 1112, and isused to control powering up of a chip for PWM control.

In one embodiment, the voltage V_(com) at the input 1132 of thecomparator 1130 isV _(com) =I _(sense) ×R _(s) −I _(—comp)×(R _(comp) +R)  (Equation 21)

The comparator 1130 sends a signal to the PWM generator 1140 for turningoff the switch 1170 if V_(com) reaches the threshold voltage V_(th) _(—)_(oc) as follows:I _(sense) ×R _(s) −I _(—comp)×(R _(comp) +R)=V _(th) _(—)_(oc)  (Equation 22)and I _(sense) ×R _(s) =V _(th) _(—) _(oc) +I _(—comp)×(R _(comp)+R)  (Equation 23)

The effective threshold signal I_(th) _(—) _(oc) is $\begin{matrix}{{I_{th\_ oc} = \frac{I_{sense}}{R_{s}}}{{Therefore},}} & \left( {{Equation}\quad 24} \right) \\{I_{th\_ oc} = {\frac{V_{th\_ oc}}{R_{s}} + \frac{I_{\_ comp} \times \left( {R_{comp} + R} \right)}{R_{s}}}} & \left( {{Equation}\quad 25} \right)\end{matrix}$

where I_(—comp) is a ramping signal whose amplitude is synchronized withthe PWM signal. Different maximum widths of the PWM signal results indifferent magnitudes for the second term in Equation 25. For example,the larger maximum width corresponds to lower input voltage, and thesmaller maximum width corresponds to higher input voltage. Accordingly,the higher input voltage results in smaller I_(th) _(—) _(oc), and thelower input voltage results in larger I_(th) _(—) _(oc). In anotherexample, the ramping signal I_(—comp) is described as follows:I _(—comp)(t)=δ×(t−nT)  (Equation 26)and 0≦t≦T_(on)  (Equation 27)

where δ is a constant, and T_(on) is the maximum width of the PWMsignal. For example, T_(on) corresponds to a period during which the PWMsignal turns on the switch 1170. In another example, a period of the PWMsignal T_(on) and T_(off) during which the PWM signal turns off theswitch 1170. In yet another example, T_(on) depends on the input voltageand the maximum current, and is represented by T_(—vin) corresponding tothe input voltage V_(in). $\begin{matrix}{{Accordingly},{{{at}\quad t} = T_{on}}} & \left( {{Equation}\quad 28} \right) \\\begin{matrix}{I_{th\_ oc} = {\frac{V_{th\_ oc}}{R_{s}} + \frac{I_{\_ comp} \times \left( {R_{comp} + R} \right)}{R_{s}}}} \\{= {\frac{V_{th\_ oc}}{R_{s}} + \frac{\delta \times T_{\_ vin} \times \left( {R_{comp} + R} \right)}{R_{s}}}}\end{matrix} & \left( {{Equation}\quad 29} \right)\end{matrix}$

For example, T_(—vin) can be expressed as follows: $\begin{matrix}{{T_{\_ vin} = \frac{V_{th\_ oc} \times L_{p}}{V_{in} \times R_{s}}}{Hence}} & \left( {{Equation}\quad 30} \right) \\{I_{th\_ oc} = {\frac{V_{th\_ oc}}{R_{s}} + \frac{\delta \times \left( {R_{comp} + R} \right) \times V_{th\_ oc} \times L_{p}}{V_{in} \times R_{s} \times R_{s}}}} & \left( {{Equation}\quad 31} \right)\end{matrix}$

As shown in Equation 31, the second term on the right side is inverselyproportional to V_(in). The effective threshold is lower for higherinput voltage and higher for lower input voltage. By adjusting theresistor 1110 of R, the effects of “delay to output” can be compensated.For example, the system 100 allows a maximum current that is constantover a wide range of the input voltage V_(in). In another example, theresistor 1110 is adjusted for given L_(p) and R_(s) in a switching modeconverter according to Equation 31.

As discussed above and further emphasized here, Equations 1-31 aremerely examples, which should not unduly limit the scope of the claims.One of ordinary skill in the art would recognize many variations,alternatives, and modifications. For example, Equations 7-31 are used todescribe certain examples for FIGS. 5-9 and 11, but FIGS. 5-9 and 11 canoperate according to methods that may be different from those ofEquations 7-31.

According to another embodiment of the present invention, a programmableline-voltage-compensated current-limiting control system and a methodthereof are provided. The line input voltage is sensed and received byan input-controlled current source. The current source generates acurrent that flows through an external resistor connecting between acurrent sensing terminal and a current sensing resistor R. The resultingoffset voltage is proportional to the line input voltage, and issuperimposed with a current sensing signal. The summation signal isprovided to an over-current comparator to generate a control signal. Thecontrol signal can be used to turn off a power switch in a switchingmode converter. For example, the system and the method are implementedaccording to the systems 500 and/or 600.

According to yet another embodiment of the present invention, aprogrammable line-voltage-compensated current-limiting control systemand a method thereof are provided. The line input voltage is sensed andreceived by an input-controlled current source. The current source flowsthrough an external resistor connecting between the current source andthe ground. The resulting offset voltage is proportional to the lineinput voltage, and is superimposed with a reference signal to generatean effective threshold signal. The effective threshold signal iscompared with a current sensing signal by an over-current comparator togenerate a control signal. The control signal can be used to turn off apower switch in a switch mode converter. For example, the system and themethod are implemented according to the system 700.

According to yet another embodiment of the present invention, aprogrammable line-voltage-compensated current-limiting control systemand a method thereof are provided. The line input voltage is sensed by aresistor and sensing transistors connecting between the line voltage anda chip power supply terminal. As a result, a current is generated thatis proportional to the line input voltage. The current is mirrored by acurrent mirror and/or a current amplifier to generate aninput-controlled current. The input-controlled current flows through anexternal resistor to generate an offset signal. For example, the systemand the method are implemented according to the systems 500, 600, and/or700.

According to yet another embodiment of the present invention, aprogrammable line-voltage-compensated current-limiting control systemand a method thereof are provided. The line input voltage is divided bya voltage divider. The divide voltage is sensed and converted to aninput-controlled current by a transconductor. The input-controlledcurrent flows through an external resistor connecting between a currentsensing terminal and a current sensing resistor. The resulting offsetvoltage is proportional to the line input voltage, and is superimposedwith a current sensing signal. The summation signal is provided to anover-current comparator to generate a control signal. The control signalcan be used to turn off a power switch in a switch mode converter. Forexample, the system and the method are implemented according to thesystem 800.

According to yet another embodiment of the present invention, aprogrammable line-voltage-compensated current-limiting control systemand a method thereof are provided. The line input voltage is divided bya voltage divider. The divide voltage is sensed and converted to aninput-controlled current by a transconductor. The input-controlledcurrent source flows through an external resistor connecting between thetransconductor and the ground. The resulting offset voltage isproportional to the line input voltage, and is superimposed with areference signal to generate an effective threshold signal. Theeffective threshold signal is compared with a current sensing signal byan over-current comparator to generate a control signal. This controlsignal can be used to turn off a power switch in a switch modeconverter. For example, the system and the method are implementedaccording to the system 900.

According to yet another embodiment of the present invention, aprogrammable line-voltage-compensated current-limiting control systemand a method thereof are provided. The line input voltage is divided bya voltage divider. The divided voltage is sensed and converted by atransconductor. As a result, a current is generated that is proportionalto the line input voltage. The current is mirrored by a current mirrorand/or a current amplifier to generate an input-controlled current. Theinput-controlled current flows through an external resistor to generatean offset signal. For example, the system and the method are implementedaccording to the systems 800 and/or 900.

According to yet another embodiment of the present invention, aprogrammable line-voltage-compensated current-limiting control systemand a method thereof are provided. The line input voltage information isrepresented by the PWM width for constant current limiting. APWM-synchronized current-ramping signal controls a current sinkconnected to a current sensing terminal of a chip. As a result, acurrent that flows through an external resistor into the chip and flowsthrough an internal resistor in the chip is sunk by the current sink.Additionally, the current has a ramping magnitude that is synchronizedwith a PWM signal. The resulting offset voltage is subtracted from acurrent sensing signal to generate a composite signal. The compositesignal is provided to an over-current comparator to generate a controlsignal. The control signal can be used to turn off a power switch in aswitch mode converter. For example, the system and the method areimplemented according to the system 1100.

According to yet another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a thresholdsignal and a first signal and to generate a comparison signal. The firstsignal is a sum of a second signal and a third signal, and the thirdsignal is associated with an input current for a power converter.Additionally, the system includes a pulse-width-modulation generatorconfigured to receive the comparison signal and generate a modulationsignal in response to the comparison signal, and a switch configured toreceive the modulation signal and control the input current for thepower converter. An amplitude for the first signal becomes larger if anamplitude for the input voltage becomes larger. The second signal isgenerated by receiving an input voltage for the power converter,converting the received input voltage to a fourth signal, and convertingthe fourth signal to the second signal. For example, the system isimplemented according to the systems 500, 600, and/or 800.

According to yet another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a firstsignal and a second signal and to generate a comparison signal. Thefirst signal is associated with an input current for a power converter.Additionally, the system includes a threshold generator configured toreceive at least a third signal and generate the second signal inresponse to at least the third signal. The third signal is associatedwith an input voltage for the power converter. Moreover, the systemincludes a pulse-width-modulation generator configured to receive thecomparison signal and generate a modulation signal in response to thecomparison signal, and a switch configured to receive the modulationsignal and control the input current for the power converter. Anamplitude for the second signal becomes smaller if an amplitude for theinput voltage becomes larger, and the third signal is generated byreceiving an input voltage for the power converter and converting thereceived input voltage to the third signal. For example, the system isimplemented according to the systems 700 and/or 900.

According to yet another embodiment, a system for protecting a powerconverter includes a first comparator configured to receive a thresholdsignal and a first signal and to generate a comparison signal. The firstsignal is equal to a second signal subtracted by a third signal, and thesecond signal is associated with an input current for a power converter.Additionally, the system includes a pulse-width-modulation generatorconfigured to receive the comparison signal and generate a modulationsignal in response to the comparison signal, and a switch configured toreceive the modulation signal and control the input current for thepower converter. Moreover, the system includes an oscillator coupled tothe pulse-width-modulation generator and configured to generate at leasta first control signal, a transconductor configured to receive the firstcontrol signal and generate a second control signal, and a currentsupplier configured to receive the second control signal and generate afirst current in response to the second control signal, the firstcurrent being associated with the third signal. An amplitude for thefirst current becomes smaller if an amplitude for the input voltagebecomes larger. For example, the system is implemented according to thesystem 1100.

According to yet another embodiment, a method for protecting a powerconverter includes receiving an input voltage for a power converter,converting the received input voltage to a first signal, converting thefirst signal to a second signal, and generating a third signal based onat least information associated with the second signal. Additionally,the method includes receiving the third signal and a threshold signal.The third signal is a sum of the second signal and a fourth signal, andthe fourth signal is associated with an input current for the powerconverter. Moreover, the method includes generating a comparison signalbased on at least information associated with the third signal and thethreshold signal, and processing information associated with thecomparison signal. Also, the method includes generating a modulationsignal based on at least information associated with the comparisonsignal, and controlling the input current for the power converter inresponse to the modulation signal. An amplitude for the third signalbecomes larger if an amplitude for the input voltage becomes larger. Forexample, the method is implemented by the systems 500, 600, and/or 800.

According to yet another embodiment, a method for protecting a powerconverter includes receiving an input voltage for a power converter,converting the received input voltage to a first signal, processinginformation associated with the first signal, generating a second signalbased on at least information associated with the first signal, andreceiving the second signal and a third signal. The third signal isassociated with an input current for a power converter. Additionally,the method includes generating a comparison signal based on at leastinformation associated with the second signal and the third signal,processing information associated with the comparison signal, generatinga modulation signal based on at least information associated with thecomparison signal, and controlling the input current for the powerconverter in response to the modulation signal. An amplitude for thesecond signal becomes smaller if an amplitude for the input voltagebecomes larger. For example, the method is implemented by the systems700 and/or 900.

According to yet another embodiment, a method for protecting a powerconverter includes generating a first signal based on at leastinformation associated with an input current for a power converter,generating a second signal, the second signal being proportional to aramping current, and processing information associated with the firstsignal and the second signal. Additionally, the method includesgenerating a third signal equal to the first signal subtracted by thesecond signal, receiving the third signal and a threshold signal,generating a comparison signal based on at least information associatedwith the third signal and the threshold signal, processing informationassociated with the comparison signal, generating a modulation signalbased on at least information associated with the comparison signal, andcontrolling the input current for the power converter in response to themodulation signal. An amplitude for the ramping current corresponding toa predetermined value for the input current becomes smaller if anamplitude for the input voltage becomes larger. For example, the methodis implemented by the system 1100.

The present invention has various applications. In some embodiments, thesystems of FIGS. 5-9 and/or 11 can be used to regulate switch-modeconverters. For example, the switch-mode converters include offlineflyback converters and/or forward converters. In other embodiments, thesystems of FIGS. 5-9 and/or 11 allow a maximum power that is constantover a wide range of input voltage.

The present invention has various advantages. Some embodiments canprovide an excellent compensation for the “delay to output” by easilyadjusting an external resistor. For example, the adjustment of theexternal resistor takes into account converter components external to achip for PWM control. Certain embodiments allow a maximum current and amaximum power that are constant over a wide range of input voltage. Someembodiments consume a low standby power by sharing a resistor for asensing system with a startup system and/or a brownout protectionsystem. For example, the resistor is shared by a sensing system and astartup system. Certain embodiments provide an excellent compensationfor the “delay to output” without sensing an input voltage. For example,the pin counts for a chip for PWM control is limited. In anotherexample, the maximum width of a PWM signal is used to represent theinput voltage. Different input voltages result in different maximumwidths for the PWM signal, and the different maximum widths result indifferent effective threshold signals. Some embodiments provide anover-current protection that can effectively protect a power converterfrom excessive power, thermal run away, excessive current and/or voltagestress.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1. A system for protecting a power converter, the system comprising: afirst comparator configured to receive a threshold signal and a firstsignal and to generate a comparison signal, the first signal being a sumof a second signal and a third signal, the third signal being associatedwith an input current for a power converter; a pulse-width-modulationgenerator configured to receive the comparison signal and generate amodulation signal in response to the comparison signal; a switchconfigured to receive the modulation signal and control the inputcurrent for the power converter; wherein: an amplitude for the firstsignal becomes larger if an amplitude for the input voltage becomeslarger; the second signal is generated by receiving an input voltage forthe power converter, converting the received input voltage to a fourthsignal, and converting the fourth signal to the second signal.
 2. Thesystem of claim 1 wherein: the power converter comprises an inductivewinding including a first end; the input current flows through theinductive winding; the input voltage is a voltage level at the firstend.
 3. The system of claim 1 wherein the input current for the powerconverter is limited to a predetermined value, the predetermined valuebeing constant over the input voltage.
 4. The system of claim 1 wherein:an input power for the power converter is limited to a predeterminedvalue; the input power is associated with the input current and theinput voltage; the predetermined value being constant over the inputvoltage.
 5. The system of claim 1 wherein the modulation signal turnsoff the switch if the comparison signal indicates an amplitude for thefirst signal is equal to or larger than an amplitude for the thresholdsignal.
 6. The system of claim 1 wherein the pulse-width-modulationgenerator comprises a pulse-width-modulation comparator, a logiccontroller, and a gate driver.
 7. The system of claim 6 wherein: thelogic controller is configured to receive the comparison signal andgenerate a control signal; the gate driver is configured to receive thecontrol signal and generate the modulation signal.
 8. The system ofclaim 1, and further comprising a first resistor configured to convertthe input current for the power converter to a first voltage, the firstvoltage being the third signal.
 9. The system of claim 8, and furthercomprising: a current supplier configured to generate a first current,the first current being associated with the input voltage for the powerconverter; a second resistor configured to convert the first current toa second voltage; wherein: the first current is the fourth signal; thesecond voltage is the second signal.
 10. The system of claim 9 whereinthe second resistor is coupled to the first resistor and the firstcomparator.
 11. The system of claim 10 wherein the second resistor isnot on a chip for pulse-width-modulation control.
 12. The system ofclaim 9, and further comprising: a third resistor configured to convertthe input voltage to a second current; a sensing system configured toreceive the second current and generate a third current in response tothe second current.
 13. The system of claim 12 wherein the currentsupplier is configured to generate the first current in response to thethird current.
 14. The system of claim 8, and further comprising: atransconductor configured to generate a first current, the first currentbeing associated with the input voltage for the power converter; asecond resistor configured to convert the first current to a secondvoltage; wherein: the first current is the fourth signal; the secondvoltage is the second signal.
 15. The system of claim 14 wherein thesecond resistor is coupled to the second resistor and the firstcomparator.
 16. The system of claim 15 wherein the second resistor isnot on a chip for pulse-width-modulation control.
 17. The system ofclaim 14, and further comprising: a voltage divider configured toreceive the input voltage and generate a third voltage; a sensing systemconfigured to receive the third voltage and generate a fourth voltage inresponse to the third voltage.
 18. The system of claim 17 wherein thetransconductor is configured to generate the first current in responseto the fourth voltage.
 19. The system of claim 17, and furthercomprising a brownout protection system coupled to the third voltage.20. A system for protecting a power converter, the system comprising: afirst comparator configured to receive a first signal and a secondsignal and to generate a comparison signal, the first signal beingassociated with an input current for a power converter; a thresholdgenerator configured to receive at least a third signal and generate thesecond signal in response to at least the third signal, the third signalbeing associated with an input voltage for the power converter; apulse-width-modulation generator configured to receive the comparisonsignal and generate a modulation signal in response to the comparisonsignal; a switch configured to receive the modulation signal and controlthe input current for the power converter; wherein: an amplitude for thesecond signal becomes smaller if an amplitude for the input voltagebecomes larger; the third signal is generated by receiving an inputvoltage for the power converter and converting the received inputvoltage to the third signal.
 21. The system of claim 20 wherein: thepower converter comprises an inductive winding including a first end;the input current flows through the inductive winding; the input voltageis a voltage level at the first end.
 22. The system of claim 20 whereinthe input current for the power converter is limited to a predeterminedvalue, the predetermined value being constant over the input voltage.23. The system of claim 20 wherein: an input power for the powerconverter is limited to a predetermined value; the input power isassociated with the input current and the input voltage; thepredetermined value being constant over the input voltage.
 24. Thesystem of claim 20 wherein the modulation signal turns off the switch ifthe comparison signal indicates an amplitude for the first signal isequal to or larger than an amplitude for the second signal.
 25. Thesystem of claim 20 wherein the pulse-width-modulation generatorcomprises a pulse-width-modulation comparator, a logic controller, and agate driver.
 26. The system of claim 25 wherein: the logic controller isconfigured to receive the comparison signal and generate a controlsignal; the gate driver is configured to receive the control signal andgenerate the modulation signal.
 27. The system of claim 20, and furthercomprising a first resistor configured to convert the input current forthe power converter to a first voltage, the first voltage being thefirst signal.
 28. The system of claim 27, and further comprising: acurrent supplier configured to generate a first current, the firstcurrent being associated with the input voltage for the power converter;a second resistor configured to convert the first current to a secondvoltage; wherein the second voltage is the third signal.
 29. The systemof claim 28 wherein the second resistor is coupled to the currentsupplier and the threshold generator.
 30. The system of claim 29 whereinthe second resistor is not on a chip for pulse-width-modulation control.31. The system of claim 30, and further comprising: a third resistorconfigured to convert the input voltage to a second current; a sensingsystem configured to receive the second current and generate a thirdvoltage in response to the second current.
 32. The system of claim 31wherein the current supplier is configured to generate the first currentin response to the third voltage.
 33. The system of claim 27, andfurther comprising: a transconductor configured to generate a firstcurrent, the first current being associated with the input voltage forthe power converter; a second resistor configured to convert the firstcurrent to a second voltage; wherein the second voltage is the thirdsignal.
 34. The system of claim 33 wherein the second resistor iscoupled to the transconductor and the threshold generator.
 35. Thesystem of claim 34 wherein the second resistor is not on a chip forpulse-width-modulation control.
 36. The system of claim 33, and furthercomprising: a voltage divider configured to receive the input voltageand generate a third voltage; a sensing system configured to receive thethird voltage and generate a fourth voltage in response to the thirdvoltage.
 37. The system of claim 36 wherein the transconductor isconfigured to generate the first current in response to the fourthvoltage.
 38. The system of claim 36, and further comprising a brownoutprotection system coupled to the third voltage.
 39. A system forprotecting a power converter, the system comprising: a first comparatorconfigured to receive a threshold signal and a first signal and togenerate a comparison signal, the first signal being equal to a secondsignal subtracted by a third signal, the second signal being associatedwith an input current for a power converter; a pulse-width-modulationgenerator configured to receive the comparison signal and generate amodulation signal in response to the comparison signal; a switchconfigured to receive the modulation signal and control the inputcurrent for the power converter; an oscillator coupled to thepulse-width-modulation generator and configured to generate at least afirst control signal; a current supplier configured to receive the firstcontrol signal and generate a first current in response to the firstcontrol signal, the first current being associated with the thirdsignal; wherein an amplitude for the first current becomes smaller if anamplitude for the input voltage becomes larger.
 40. The system of claim39 wherein: the power converter comprises an inductive winding includinga first end; the input current flows through the inductive winding; theinput voltage is a voltage level at the first end.
 41. The system ofclaim 39 wherein the input current for the power converter is limited toa predetermined value, the predetermined value being constant over theinput voltage.
 42. The system of claim 39 wherein: an input power forthe power converter is limited to a predetermined value; the input poweris associated with the input current and the input voltage; thepredetermined value being constant over the input voltage.
 43. Thesystem of claim 39 wherein the modulation signal turns off the switch ifthe comparison signal indicates an amplitude for the first signal isequal to or larger than an amplitude for the threshold signal.
 44. Thesystem of claim 39 wherein the pulse-width-modulation generatorcomprises a pulse-width-modulation comparator, a logic controller, and agate driver.
 45. The system of claim 44 wherein: the logic controller isconfigured to receive the comparison signal and generate a secondcontrol signal; the gate driver is configured to receive the secondcontrol signal and generate the modulation signal.
 46. The system ofclaim 39, and further comprising a first resistor configured to convertthe input current for the power converter to a first voltage, the firstvoltage being the second signal.
 47. The system of claim 46, and furthercomprising a second resistor configured to convert the first current toa second voltage.
 48. The system of claim 47 wherein the second resistoris not on a chip for pulse-width-modulation control.
 49. The system ofclaim 47, and further comprising: a third resistor configured to convertthe first current to a third voltage; wherein a sum of the secondvoltage and the third voltage is the third signal.
 50. The system ofclaim 49 wherein: the second resistor is coupled to the first resistorand the third resistor; the third resistor is coupled to the secondresistor and the first comparator.
 51. A method for protecting a powerconverter, the method comprising: receiving an input voltage for a powerconverter; converting the received input voltage to a first signal;converting the first signal to a second signal; generating a thirdsignal based on at least information associated with the second signal;receiving the third signal and a threshold signal, the third signalbeing a sum of the second signal and a fourth signal, the fourth signalbeing associated with an input current for the power converter;generating a comparison signal based on at least information associatedwith the third signal and the threshold signal; processing informationassociated with the comparison signal; generating a modulation signalbased on at least information associated with the comparison signal;controlling the input current for the power converter in response to themodulation signal; wherein an amplitude for the third signal becomeslarger if an amplitude for the input voltage becomes larger.
 52. Amethod for protecting a power converter, the method comprising:receiving an input voltage for a power converter; converting thereceived input voltage to a first signal; processing informationassociated with the first signal; generating a second signal based on atleast information associated with the first signal; receiving the secondsignal and a third signal, the third signal being associated with aninput current for a power converter; generating a comparison signalbased on at least information associated with the second signal and thethird signal; processing information associated with the comparisonsignal; generating a modulation signal based on at least informationassociated with the comparison signal; controlling the input current forthe power converter in response to the modulation signal; wherein anamplitude for the second signal becomes smaller if an amplitude for theinput voltage becomes larger.
 53. A method for protecting a powerconverter, the method comprising: generating a first signal based on atleast information associated with an input current for a powerconverter; generating a second signal, the second signal beingproportional to a ramping current; processing information associatedwith the first signal and the second signal; generating a third signalequal to the first signal subtracted by the second signal; receiving thethird signal and a threshold signal; generating a comparison signalbased on at least information associated with the third signal and thethreshold signal; processing information associated with the comparisonsignal; generating a modulation signal based on at least informationassociated with the comparison signal; controlling the input current forthe power converter in response to the modulation signal; wherein anamplitude for the ramping current corresponding to a predetermined valuefor the input current becomes smaller if an amplitude for the inputvoltage becomes larger.